Shotshell or shotgun cartridges typically comprise a propellant charge, a wad and a shot load, all of which are contained within a plastic or paper shell reinforced at one end with a metal case head to contain and direct the created propellant gases through the opposite end of the cartridge. The shotgun wad typically comprises an injection molded polymer body that obturates against the barrel during firing to prevent escape of propellant gases around the slug or through the shot. The wad often comprises a forward facing cup portion with wings that contains the shot or slug as the shot travels through the barrel. Upon exiting the barrel, aerodynamic drag on the cup portion or the flaring of the fins slows the wad separating the wad from the slug or shot and freeing the projectile(s) to travel onto the target alone.
A primary consideration is determining the performance of a shot loaded shotshell cartridge is determining the maximum effective range at which there is sufficient shot density to accurately strike a target. A standard measurement for determining the effective range of the shotgun cartridge is patterning or measuring the percentage of shot that strikes within a 30 inch circle at 40 yards or other predetermined distance. The tightness of the pattern or the percentage of shot that strikes within the circle can be affected by the size and shape of the shot, the size of the propellant load and the separation point between the wad and the shot. For the purposes of this disclosure, the separation point is the point during flight in which wad dispenses the shot load from the cup portion. To the extent that the separation point can be delayed, the effective range can be extended. However, in conventional wads, the longer the wad remains with the shot during flight, the greater the likelihood that the wad flight will be unstable and will yaw or otherwise have a non-straight flight and will worsen the patterning of the shot load or produce an irregular shot pattern.
Thus the forward wings on the shot cup that deploy almost immediately after leaving the muzzle causing significant aerodynamic drag upon leaving the muzzle with n intended separation point as close to the end of the muzzle as possible.
In certain wads, the wad is commonly formed by four separate wings together defining the walls of the forward cup. The wings flare open immediately upon leaving the muzzle to slow the wad and release the load as soon as possible. Similarly, certain shotgun chokes, such as disclosed in U.S. Pat. No. 7,523,581, slow the wad as the wad passes the choke to begin to separate the shot from the load even before the wad exits the muzzle. In both configurations, the wad is rapidly slowed to facilitate a separation point as close to the muzzle of the barrel as possible.
U.S. Pat. No. 6,260,484 provided a meaningful advancement in maintaining flight stability of the wad with shot permitting wad separation further down the flight path. This is commercially sold as the FLIGHTCONTROL® wad. Referring to FIGS. 1 and 2, a wad 30 as disclosed in the '484 patent is depicted. The wad design provides a dual cup, with a forward shot cup portion 32 and a rearward propellant cup portion 34. The propellant cup portion with fins 40 flares when the wad with shot leaves the muzzle due to high muzzle pressure behind the wad, see FIG. 3. Initially, the high propellant gas pressure as the wad and shot are leaving the barrel is sufficient to momentarily fold the fins forward. The fins then retract to a flared flight position where the fins slow the wad down releasing the shot. The flaring is facilitated by axial cuts 42 in the propellant cup. The flared fins provide stabilization of the wad with shot traveling down the flight path. Additionally, wall segments 44 in the forward shot cup portion open for providing compaction relief of the shot in the shot cup portion facilitating even dispersal and more consistent shot departure from the shot cup. Several manufacturers have adopted features disclosed in the '484 patent. The '484 patent is owned by the applicant of the instant application and is incorporated by reference herein for all purposes.
It has been recognized that different shotgun shells which utilize the rear cup portion fins and the side opening window as disclosed in the U.S. Pat. No. 6,260,484 often exhibit inconsistent patterns when the cartridges are fired in shotguns with ported chokes. See FIG. 4 which represents the failure of the fins to deploy and the resulting instability of the wad and shot. Also, refer to FIG. 5 that illustrates the reduced barrel pressure 48 available to deploy fins at the wad and shot exit point compared to non-choked pressures 50.
See also US 2013/0228090, owned by the owner of the instant application and incorporated herein by reference addressing the advantages of separating the center of pressure and the center of gravity for wad flight stability and certain advantages of using different polymers for the forward shot cup and rearward propellant cup.